Biology Midterm Review
Phospholipids are amphiphilic. The two inside tails are hydrophobic, and the outside head is hydrophilic. They
help make up the lipid bilayer, and control what substances leave and enter the cell. The lipid bilayer affects
the fluidity of the membrane, and movement of the membrane. Lower temperatures cause the bilayer to be
packed tightly, and this restricts the movement. Higher temperatures cause the bilayer to be more fluid, so
the movement of the membrane increases.
Fatty acids are non-polar and insoluble in water. Saturated fatty acids (animal fats) have no double bonds and
no kinks, and they also tend to be solid at room temperature because they can bond together quite well. A
higher concentration of saturated fatty acids in membranes cause the membrane to be less fluid, and this
causes the melting point of the membrane to increase.
Types of molecules that can freely cross membranes: small and hydrophobic molecules such as O , H2O,2CO 2
Types of molecules that cannot freely cross membranes: any molecules soluble in water such as ions and
Bacteria, archae and eukarya all have the same common ancestor.
Eukaryotes evolved from the infolding of the plasma membrane, which helped create the ER and nuclear
envelope. Internal membranous organelles were the result of endosymbiotic events. Aerobic prokaryotes
(bacteria) invaded the invaginations in the cell, and became mitochondria.
Eukaryotes: larger cells with a nucleus and membrane-bound organelles (such as mitochondria), has a
cytoskeleton, divides via mitosis or meiosis
Prokaryotes: smaller cells without a nucleus and no membrane-bound organelles, has no cytoskeleton, divides
via binary fission
Animal cells: dont have chloroplasts, one or more small vacuoles, dont have plastids or cell walls, have
lysosomes, is an irregular round shape
Plant cells: have chloroplasts, one very large vacuole, have plastids and cell walls, usually doesnt have
lysosomes, is a fixed rectangular shape
Chloroplasts: used for photosynthesis - traps energy from sunlight
Endoplasmic reticulum: used in translation and folding of new proteins (rough endoplasmic reticulum),
expression of lipids (smooth endoplasmic reticulum)
Golgi apparatus: sorts and modifies proteins
Mitochondria: energy production from the oxidation of food substances and the release of ATP
Vacuole: used for storage and maintaining homeostasis
Nucleus: involved in DNA maintenance, it controls all activities of the cell and RNA transcription
Cytoskeleton: system of wires and pullies inside the cell, important for mobility, communication and very
important in cell division (moving chromosomes and organelles around)
Light micrographs can be in colour and do not magnify the cells significantly.
Electron micrographs cannot be in colour and magnify the cells dramatically.
Chromosomes in prokaryotes are circular in shape.
Chromosomes in eukaryotes are linear.
Eukaryotes fire off multiple replication origins at a time. Prokaryotes only have one replication origin.
Binary fission ensures that daughter cells get one original copy of the chromosome.
DNA replication and chromosome replication are the same thing in prokaryotes. When a eukaryote replicates
its DNA, it doesnt increase the number of chromosomes that it has.
The number of chromosomes does not change in the cell cycle, it only changes at the end of meiosis.
G0 phase: when cells are not involved in the cell cycle, they are just doing their intended job
G1 phase: cell grows
G1 checkpoint: gives the cell time to prepare for the next phase and fixes any damage to DNA
S phase: the DNA replicates and chromosomal proteins are duplicated
G2 phase: prepares the cell for division
G2 checkpoint: ensures the cell is big enough and ready for mitosis Cell cycle checkpoints are to make sure everything is working smoothly and make sure daughter cells get the
proper number and properly copied chromosomes.
Mitosis replicates the cells to create daughter cells.
Interphase: the cell prepares for mitosis
Prophase: the chromatin condense into visible chromosomes
Prometaphase: microtubules invade fragmented nucleus and spindles attach to the kinetochores of the
Metaphase: chromosomes align at the central plate
Cell cycle checkpoint after metaphase wont proceed until all chromosomes are attached to the spindle
Anaphase: the chromatids separate
Telophase: the separated chromatids reach opposite sides of the cell and then micro filaments made of
actin, constrict the cell so the cell can divide
Cytokinesis: the cells divide
Ploidy: the number of sets of chromosomes in a cell
Chromatin: the combination of DNA and proteins that make up the contents of the nucleus of a cell.
Chromosomes: a single piece of coiled DNA and protein found in cells.
Chromatids: two identical copies of DNA making up a duplicated chromosome, which are joined at their
DNA: makes up the chromatin, chromosomes and chromatids
Ploidy: controls the amount of chromatin, chromosomes, chromatids, and DNA is present in a cell
The cytoskeleton ensures that all the chromosomes get into the daughter cells.
Mitosis is very important in development and growth, cell replacement, regeneration, and asexual
Microtubules are made of tubulin. Microfilaments are made of actin. Intermediate filaments are made of
keratin. These three parts of the cytoskeleton work together to enhance structural integrity, cell shape, and
cell and organelle movement. They are very important in moving around chromosomes, maintaining the
shape of the cell, and dividing the cell in mitosis.
DNA replication is not 100% precise; once in a while a mistake will occur, changing the gene sequence, giving a
new version of a gene which i